Chromatography is a widely used analytical technique for the chemical analysis and separation of molecules. Chromatography involves the separation of one or more analyte species from other matrix components present in a sample. A stationary phase of a chromatography column is typically selected so that there is an interaction with the analyte. Such interactions can be ionic, hydrophilic, hydrophobic, or a combination thereof. For example, the stationary phase can be derivatized with ionic moieties that ideally will bind to ionic analytes and matrix components with varying levels of affinity. A mobile phase is percolated through the stationary phase and competes with the analyte and matrix components for binding to the ionic moieties. The mobile phase or eluent are terms used to describe a liquid solvent or buffer solution that is pumped through a chromatography column. During this competition, the analyte and matrix components will elute off of the stationary phase as a function of time and then be subsequently detected at a detector. Examples of some typical detectors are a conductivity detector, a UV-VIS spectrophotometer, and a mass spectrometer. Over the years, chromatography has developed into a powerful analytical tool that is useful for creating a healthier, cleaner, and safer environment where complex sample mixtures can be separated and analyzed for various industries such as water quality, environmental monitoring, food analysis, pharmaceutical, and biotechnology.
In regards to water quality, haloacetic acids are a group of disinfection byproducts resulting from the reaction between naturally occurring organic matter and the disinfectants used during water treatment. The presence of haloacetic acids in drinking water has been linked to several adverse effects including bladder, kidney, and colorectal cancer. Contemporaneous with this filing, five haloacetic acids (HAA5) are currently regulated at the total level of 60 μg/L by the US Environmental Protection Agency (EPA), which are monochloroacetic acid (MCAA), dichloroacetic acid (DCAA), trichloroacetic acid (TCAA), monobromoacetic acid (MBAA), dibromoacetic acid (DBAA). There are also four other haloacetic acids bromochloroacetic acid (BCAA), bromodichloroacetic acid (BDCAA), dibromochloroacetic acid (DBCAA), and tribromoacetic acid (TBAA)) that are not currently regulated, but are on the Unregulated Contaminant Monitoring Rule (UCMR) 4 list for monitoring by public water systems between 2018 and 2020. Collectively, the above noted nine haloacetic acids may be referred to with the acronym HAA9.
In addition, a group of common inorganic anions are routinely monitored in drinking water. For example, the National Primary Drinking Water Standards in the United States specify a Maximum Contaminant Level (MCL) for a number of inorganic anions such as fluoride, nitrite, and nitrate. The MCLs are specified to minimize potential health effects arising from the ingestion of these anions in drinking water. High levels of fluoride cause skeletal and dental fluorosis, and nitrite and nitrate can cause methemoglobulinemia, which can be fatal to infants. Other common anions, such as chloride and sulfate, are considered secondary contaminants. The National Secondary Drinking Water Standards in the U.S. are guidelines regarding taste, odor, color, and certain aesthetic characteristics. Although these guidelines are not federally enforced, they are recommended to all states as reasonable goals and many states adopt their own regulations governing these contaminants
Under certain circumstances, anion exchange stationary phases can have different affinity values to haloacetic acids and common inorganic anions, which makes analysis of both types of chemicals difficult during a single chromatographic run. When the retention times of various haloacetic acids and common inorganic anions are sufficiently different, the time required for a single chromatographic run can be unacceptably long. To simplify the analysis of water quality for more than one group of anions, Applicant believes that there is a need for anion exchange stationary phases that require relatively low eluent concentrations and can separate and resolve both haloacetic acids and common inorganic anions in a single relatively fast chromatographic run.
Water samples containing haloacetic acids can have a relatively high ionic strength matrix (e.g., chloride, sulfate, carbonate, and nitrate) that can make the measurement of multiple haloacetic acids challenging. Methods that have been developed for chromatographically measuring haloacetic acids typically require a sample pre-treatment step. As such, Applicant believes that there is a need to measure nine haloacetic acids in a single chromatography run where the sample has a relatively high ionic strength matrix without pre-treating the sample beforehand to remove a portion of the high ionic strength matrix.